1. Field of the Invention
The invention relates to a semiconductor light source lighting circuit for lighting a semiconductor light source such as an LED (Light Emitting Diode).
2. Related Art
In recent years, an LED having a longer life and lower power consumption has been used as a vehicular lamp such as a headlamp, instead of a conventional halogen lamp having a filament. Since a degree of light emission (e.g. a brightness) of the LED depends on a current flowing through the LED, it is necessary to provide a lighting circuit for adjusting the current flowing through the LED in order to use the LED as a light source.
Such a lighting circuit usually includes a switching regulator for generating the current flowing through the LED using a switching element and a control circuit for controlling the switching regulator. The control circuit includes an error amplifier and performs a feedback control such that the current flowing through the LED is to be stable (see, for example, JP-A-2010-170704).
In order to reduce a circuit size by improving a performance of the feedback control, a digitization of the control circuit may be conceivable. However, as a result of the digitization, there may be a possibility that an oscillation occurs in the current flowing through the LED by an interaction between a counting operation in the feedback control and a switching operation of the switching regulator.